Fixed torque spring clutch

Abstract

A fixed torque spring clutch has first and second rotors. The torque of the first rotor is transmitted to the second rotor via a coil spring. The second rotor is coaxial with the first rotor. A shaft section is provided on one of the rotors. A plurality of catch sections are provided on the other rotor. The coil spring is mounted over the shaft section. The two ends of the coil spring are caught by the catch sections in a clamping state of the clutch. The coil spring has a first clamping section for clamping the shaft section with a predetermined clamping force when the coil spring is mounted over the shaft section, and a second clamping section having a clearance with respect to the corresponding part of the shaft section when the coil spring is mounted thereon.

What is claimed is: 
     
       1. A fixed torque spring clutch comprising: a first rotor;   a second rotor coaxial with said first rotor;   a shaft section on one of said rotors;   a plurality of catch sections on the other rotor; and   a coil spring covering said shaft section, said coil spring having a first end engaging one of said catch sections and a second end engaging another of said catch sections, to define a first state of said coil in which said coil has a diameter that is less than the diameter thereof in the absence of engagement of said first and second ends and catch sections, said coil spring being divided into a first clamping section which clamps said shaft section with a predetermined force in the first state, and a second clamping section which has a clearance with respect to said shaft section in said first state,   whereby the torque T transmitted between said rotors via said coil spring, is equal to T 1  -T 2 , wherein T 1  is an elastic force between said one catch section and said first end of said coil spring and T 2  is an elastic force between said another catch section and said second end of said coil spring, when one of said rotors is rotated with respect to the other of said rotors.   
     
     
       2. The fixed torque spring clutch according to claim 1, wherein the cross section of the wire forming said coil spring has a flat face, and said flat face is directed toward the outer circumferential face of said shaft section. 
     
     
       3. The fixed torque spring clutch according to claim 1, wherein the inner diameters of said first and second clamping sections of said coil spring are larger than the diameter of said shaft section before said coil spring covers said shaft section. 
     
     
       4. The fixed torque spring clutch according to claim 3, wherein the cross section of the wire forming said coil spring has a flat face, and said flat face is directed toward the outer circumferential face of said shaft section. 
     
     
       5. A fixed torque spring clutch comprising: a first rotor;   a second rotor coaxial with said first rotor;   a hollow cylindrical shaft section on one of said rotors;   first and second catch sections on the other rotor; and   a coil spring positioned in said shaft section, said coil spring having a first end engaging one of said catch sections and a second end engaging another of said catch sections, to define a first state of said coil in which said coil has a diameter that is greater than the diameter thereof in the absence of engagement of said first and second ends and catch sections, said coil spring being divided into a first clamping section which elastically clamps the inner face of said shaft section in said first state, and a second clamping section which has a clearance with respect to said shaft section in said first state.   whereby the torque T transmitted between said rotors via said coil spring, is equal to T1-T2, wherein T1 is an elastic force between said first catch section and said first end of said coil spring and T2 is an elastic force between said second catch section and said second end of said coil spring, when one of said rotors is rotated with respect to the other of said rotors.   
     
     
       6. The fixed torque spring clutch according to claim 5 wherein the cross section of the wire forming said coil spring has a flat face, and said flat face is directed toward the inner face of said shaft section. 
     
     
       7. The fixed torque spring clutch according to claim 5, wherein the outer diameters of said first and second clamping sections of said coil spring are smaller than the diameter of said shaft section before said coil spring is provided in said shaft section. 
     
     
       8. The fixed torque spring clutch according to claim 7 wherein the cross section of the wire forming said coil spring has a flat face, and said flat face is directed toward the inner face of said shaft section. 
     
     
       9. A winder having a reel for winding a tape, a string, or a wire, and means for driving the reel, comprising: a first rotor;   a second rotor coaxial with said first rotor;   said reel being coupled to one of said rotors;   a shaft section on one of said rotors;   a plurality of catch sections on the other rotor; and   a coil spring covering said shaft section, said coil spring having a first end engaging one of said catch sections and a second end engaging another of said catch sections, to define a first state of said coil in which said coil has a diameter that is less than the diameter thereof in the absence of engagement of said first and second ends and catch sections, said coil spring being divided into a first clamping section which clamps said shaft section with a predetermined force in the first state , and a second clamping section which has a clearance with respect to said shaft section in said first state,   whereby the torque T transmitted between said rotors via said coil spring, is equal to T 1  -T 2 , wherein T 1  is an elastic force between said one catch section and said first end of said coil spring and T 2  is an elastic force between said another catch section and said second end of said coil spring, when one of said rotors is rotated with respect to the other of said rotors.   
     
     
       10. The winder according to claim 9, wherein the cross section of the wire forming said coil spring has a flat face, and said flat face is directed toward the outer circumferential face of said shaft section. 
     
     
       11. The winder according to claim 9, wherein the inner diameter of said first and second clamping sections of said coil spring are larger than the diameter of said shaft section before said coil spring is provided over said shaft section. 
     
     
       12. The winder according to claim 11, wherein the cross section of the wire forming said coil spring has a flat face, and said flat face is directed toward the outer circumferential face of said shaft section. 
     
     
       13. A winder having a reel for winding a tape, a string, or a wire and means for driving the reel, comprising: a first rotor;   a second rotor coaxial with said first rotor;   said reel being coupled to one of said rotors;   a hollow cylindrical shaft section on one of said rotors;   first and second catch sections on the other rotor; and   a coil spring positioned in said shaft section, said coil spring having a first end engaging one of said catch sections and a second end engaging another of said catch sections, to define a first state of said coil in which said coil has a diameter that is greater than the diameter thereof in the absence of engagement of said first and second ends and catch sections, said coil spring being divided into a first clamping section which elastically clamps the inner face of said shaft section in said first state, and a second clamping section which has a clearance with respect to said shaft section in said first state   whereby the torque T transmitted between said rotors via said coil spring, is equal to T1 -T2, wherein T1 is an elastic force between said first catch section and said first end of said coil spring and T2 is an elastic force between said second catch section and said second end of said coil spring, when one of said rotors is rotated with respect to the other of said rotors.   
     
     
       14. The winder according to claim 13 wherein the cross section of the wire forming said coil spring has a flat face, and said flat face is directed toward the inner face of said shaft section. 
     
     
       15. The winder according to claim 13, wherein the outer diameter of said first and second clamping sections of said coil spring is smaller than the inner diameter of said shaft section before said coil spring is provided in said shaft section. 
     
     
       16. The winder according to claim 15, wherein the cross section of the wire forming said coil spring has a flat face, and said flat face is directed toward the inner face of said shaft section.